The Geochronology Of Pan-African Granite-gneiss From Nierong Micro-Landmass, Qinghai-Tibet Plateau

At present, the international circles of geoscience attention Gondwanaland formation and the decomposition causes the research of the Pre-Cambrian period significant geology event to become the hot spot once more.The predecessor yielded the remarkable gradual result in the nierong micro landmass research, the nierong piece hemp mixed crag the age data which has has prompted our nierong micro landmass is very possibly a post Vannes system part, therefore about nierong micro landmass basis nature whether belongs to the Pan-African basis already to become the scientific front question which urgently awaits to be solved.Nierong Micro-Landmass, Geographical is subordinate to Naqu region TAR, Geotecture is a large micro-lens gripping Gangdese plate of northern Tibet and Qiangtang plate in Bangong Lake-Nujiang suture zone, the southern boundary is Ganong-Jiayuri-Nima-xiaqiuka and by the main fracture of Bangong Lake-Nujiang plate suture zone for nouthern boundary (picture 2.2). Nierong Micro-Landmass exposure structure formation outcrop were Precambrian, Paleozoic, Jurassic, and lithostratigraphy department of carboniferous, Permian, Triassic, Jurassic, Cretaceous, Paleogene, Neogene and Quaternary. The stratum distribution is very uneven, the east-west extension is relatively stable, changes significantly from north to south. Nierongrong rock group is the oldest on Nierong Micro-Landmass, mainly distributed in the Cuonacuo, Lassie, Lalongduo, and Zhama area. As the previous studies is lower, there is a big know difference in the structure properties and the times of Nierong metamorphic terrane, different scholars have different names. About this Nierong gneiss age, known isotopic age:U-Pb zircon ages 519±12Ma (Xu Ronghua,1993), Zircon age of 530Ma (Chang chengfa,1986),2000Ma (Chang chengfa,1988). Recently access to the following new age in Amdo County:Nierong rock group has the Sm-Nd isochron age of 600Ma, Intrusive in the Nierong rock groups tonalitic gneisses have two zircon U-Pb ages of 491±1Ma and 492±1Ma. the same samples of gneissic monzogranite obtained two sets age, respectively 814±18Ma and 515±14Ma. The isotopic age of the most frequent is 500-800Ma, is from Sinian to Cambrian.Despite in the early 1950 years was carried out geological studies, until the late 70s have a system of regional geological data, and Tibet Geological Bureau, Chinese Academy of Sciences, Chinese Academy of Geological Sciences, Bureau of Geology and Mineral Resources of Tibet, China University of Geosciences and a number of units and collective depth surveys and research the area. However, There are still many outstanding issues about Nierong rock group and Understanding of micro-continental block structural properties, Primary cause:(1) Low level of previous studies, significant differences understanding of structural properties to Nierong rock group and micro-continental block; (2) Limited by the test conditions and the lack of research data on zircon, these ages have not been well explained and used, the geological significance become blurred; (3) When the previous establish structural stratigraphic unit, mainly based on lithological characteristics, lack of fossil data; (4) The lack of precise age data, Geochronology research is critical, Including the basement structure, formation and evolution, structure overlap and other rich time constraint information.The paper select the Nierong Micro-Landmass of the northern margin of Lhasa plateau, as key research areas, on the basis of the full understanding and knowledge of previous information and research results, by a detailed geological survey of Nierong Micro-Landmass, systemly collected of the rock samples, Use of high-precision isotopic dating methods LA-ICP-MS, etc. Access to a number of high-precision isotopic age data, with the morphological characteristics of zircon, cathodoluminescence,transmitted light,reflection Image feature, access to three Amdo region of biotite plagioclase gneiss samples,79 zircon cathodoluminescence and rare earth, trace element characteristics reveal: zircon has typical of magmatic crystallization characteristics, represent the intrusion of Pan-African age. Access to Amdo region of biotite plagioclase gneiss's zircon U-Pb isotopic age:505零3 Ma,505±5 Ma, Biotite gneiss zircon U-Pb isotopic age of 488±4 Ma, Granitic gneiss zircon U-Pb isotopic age of 505±4 Ma, belongs to the late Cambrian, Is the Pan-African-Early Paleozoic events in chronological record.Research also received Biotite Ar-Ar plateau age tp=167±1 Ma of biotite gneiss, This age represents the two-feldspar gneiss, biotite cooling age of uplift process, the original rock gneiss metamorphism and deformation events occurred near the surface should be uplifted to the Middle Jurassic Bathonian Bajocian period, it is the same to Jurassic magmatism age on Nierong Micro-Landmass.The study was in the northern gangdese plate and southern qiangtang plate, Nierong Micro-Landmass is same of the basement complex rocks in Himalayan region, Laguigangri areas, kaqiong regions and Amdo-Nierong regions, department of the Al-rich metasedimentary rocks and granitic gneiss, Generally,there are marble, metamorphism and deformation is the same, and get biotite plagioclase gneiss intrusion age is in the late Cambrian, belong to Pan-African magmatic activity recorded, This is further evidence, Pan-African movement of the affected areas's north at least can be extended to gangdese-nyenchen tanglha plate's north, even extending to the South Qiangtang-Baoshan minor continental blocks.